EP 2 387 963 A1 discloses a temperature distribution determining apparatus for determining a temperature distribution within an object caused by applying energy to the object. The apparatus comprises a temperature distribution measuring unit for measuring a spatially and temporally dependent first temperature distribution in the object, while the energy is applied to the object such that the object is heated to a temperature within a first temperature range. The apparatus further comprises a temperature distribution estimating unit for estimating a spatially and temporally dependent second temperature distribution in the object within a second temperature range, which is different to the first temperature range, based on the spatial and temporal dependence of the measured first temperature distribution.